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Date:   Sun, 21 May 2023 22:19:44 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>
cc:     Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
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        Qi Zheng <zhengqi.arch@bytedance.com>,
        Yang Shi <shy828301@gmail.com>,
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        Ira Weiny <ira.weiny@intel.com>,
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        Axel Rasmussen <axelrasmussen@google.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
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        Minchan Kim <minchan@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Song Liu <song@kernel.org>,
        Thomas Hellstrom <thomas.hellstrom@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH 23/31] mm/mglru: allow pte_offset_map_nolock() to fail
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MGLRU's walk_pte_range() use the safer pte_offset_map_nolock(), rather
than pte_lockptr(), to get the ptl for its trylock.  Just return false
and move on to next extent if it fails, like when the trylock fails.
Remove the VM_WARN_ON_ONCE(pmd_leaf) since that will happen, rarely.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
 mm/vmscan.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d257916f39e5..1c344589c145 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3992,15 +3992,15 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 	struct pglist_data *pgdat = lruvec_pgdat(walk->lruvec);
 	int old_gen, new_gen = lru_gen_from_seq(walk->max_seq);
 
-	VM_WARN_ON_ONCE(pmd_leaf(*pmd));
-
-	ptl = pte_lockptr(args->mm, pmd);
-	if (!spin_trylock(ptl))
+	pte = pte_offset_map_nolock(args->mm, pmd, start & PMD_MASK, &ptl);
+	if (!pte)
 		return false;
+	if (!spin_trylock(ptl)) {
+		pte_unmap(pte);
+		return false;
+	}
 
 	arch_enter_lazy_mmu_mode();
-
-	pte = pte_offset_map(pmd, start & PMD_MASK);
 restart:
 	for (i = pte_index(start), addr = start; addr != end; i++, addr += PAGE_SIZE) {
 		unsigned long pfn;
@@ -4041,10 +4041,8 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 	if (i < PTRS_PER_PTE && get_next_vma(PMD_MASK, PAGE_SIZE, args, &start, &end))
 		goto restart;
 
-	pte_unmap(pte);
-
 	arch_leave_lazy_mmu_mode();
-	spin_unlock(ptl);
+	pte_unmap_unlock(pte, ptl);
 
 	return suitable_to_scan(total, young);
 }
-- 
2.35.3